Objective:To analyze the effect of nucleotide sequence variants in the 5′ untranslated region (5′UTR) of Helicobacter pylori (Hp) cagA on mRNA secondary structure, as well as its regulatory role in cytotoxin-associated gene A (CagA) protein expression and bacterial virulence. Methods:The upstream nucleotide sequence of cagA was amplified by polymerase chain reaction (PCR) from 37 Hp strains, and the PCR products were sequenced. MEGA 5.0 software and RNAfold prediction software were used to analyze the nucleotide sequence variants of cagA 5′UTR and the changes in mRNA secondary structure of this region, respectively. Western blot was used to detect the expression level of CagA protein in Hp strains, and the regulatory effect of cagA 5′UTR variants on the difference in CagA protein expression was analyzed. An Hp-infected AGS cell model was established to evaluate bacterial adhesion rate; quantitative PCR (qPCR) was used to analyze the mRNA transcription levels of interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α); enzyme-linked immunosorbent assay (ELISA) was used to detect the secretion levels of IL-8 and TNF-α proteins. Results:Nucleotide sequence alignment of cagA 5′UTR from 37 Hp strains showed that sequence differences were mainly concentrated in the -53motif, -10motif, + 34motif, and + 86motif regions. mRNA secondary structure prediction analysis revealed three types based on the StemB stem-loop structure: type Ⅰ (no StemB stem-loop), type ⅡA (StemB stem-loop with 3-4 base partial pairing), and type ⅡB (StemB stem-loop with 5 base full pairing). Western blot analysis showed that the CagA protein expression level was the highest in type Ⅰ Hp strains (1.72±0.29) and the lowest in type ⅡB strains (0.81±0.26), with a statistically significant difference between the two types ( P=0.030). The adhesion rate of type Ⅰ Hp strains to AGS cells was (52.90±11.17)%, which was higher than that of type Ⅱ strains [(21.27±6.16)%]. qPCR results showed that the mRNA transcription levels of IL-8 and TNF-α in AGS cells induced by type Ⅰ Hp strains were higher than those induced by type Ⅱ strains (140.23±24.47 vs 76.16±8.76, P=0.069; 55.20±9.04 vs 21.26±6.16, P=0.036). ELISA analysis further indicated that the secretion levels of IL-8 and TNF-α proteins in AGS cells induced by type Ⅰ Hp strains were also higher than those induced by type Ⅱ strains [(344.66±62.62)pg/ml vs (302.13±66.27)pg/ml, P=0.665; (131.04±4.94)pg/ml vs (79.17±11.32)pg/ml, P=0.014]. Conclusions:The cagA 5′UTR region of Hp strains exhibits significant nucleotide sequence variants. Hp strains with no StemB stem-loop (type Ⅰ) in the mRNA secondary structure show significantly increased CagA protein expression and higher bacterial pathogenic potential.

Objective:To analyze the effect of nucleotide sequence variants in the 5′ untranslated region (5′UTR) of Helicobacter pylori (Hp) cagA on mRNA secondary structure, as well as its regulatory role in cytotoxin-associated gene A (CagA) protein expression and bacterial virulence. Methods:The upstream nucleotide sequence of cagA was amplified by polymerase chain reaction (PCR) from 37 Hp strains, and the PCR products were sequenced. MEGA 5.0 software and RNAfold prediction software were used to analyze the nucleotide sequence variants of cagA 5′UTR and the changes in mRNA secondary structure of this region, respectively. Western blot was used to detect the expression level of CagA protein in Hp strains, and the regulatory effect of cagA 5′UTR variants on the difference in CagA protein expression was analyzed. An Hp-infected AGS cell model was established to evaluate bacterial adhesion rate; quantitative PCR (qPCR) was used to analyze the mRNA transcription levels of interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α); enzyme-linked immunosorbent assay (ELISA) was used to detect the secretion levels of IL-8 and TNF-α proteins. Results:Nucleotide sequence alignment of cagA 5′UTR from 37 Hp strains showed that sequence differences were mainly concentrated in the -53motif, -10motif, + 34motif, and + 86motif regions. mRNA secondary structure prediction analysis revealed three types based on the StemB stem-loop structure: type Ⅰ (no StemB stem-loop), type ⅡA (StemB stem-loop with 3-4 base partial pairing), and type ⅡB (StemB stem-loop with 5 base full pairing). Western blot analysis showed that the CagA protein expression level was the highest in type Ⅰ Hp strains (1.72±0.29) and the lowest in type ⅡB strains (0.81±0.26), with a statistically significant difference between the two types ( P=0.030). The adhesion rate of type Ⅰ Hp strains to AGS cells was (52.90±11.17)%, which was higher than that of type Ⅱ strains [(21.27±6.16)%]. qPCR results showed that the mRNA transcription levels of IL-8 and TNF-α in AGS cells induced by type Ⅰ Hp strains were higher than those induced by type Ⅱ strains (140.23±24.47 vs 76.16±8.76, P=0.069; 55.20±9.04 vs 21.26±6.16, P=0.036). ELISA analysis further indicated that the secretion levels of IL-8 and TNF-α proteins in AGS cells induced by type Ⅰ Hp strains were also higher than those induced by type Ⅱ strains [(344.66±62.62)pg/ml vs (302.13±66.27)pg/ml, P=0.665; (131.04±4.94)pg/ml vs (79.17±11.32)pg/ml, P=0.014]. Conclusions:The cagA 5′UTR region of Hp strains exhibits significant nucleotide sequence variants. Hp strains with no StemB stem-loop (type Ⅰ) in the mRNA secondary structure show significantly increased CagA protein expression and higher bacterial pathogenic potential.

Objective To analyze the single resistance and multiple resistance situation of of Helicobacter pylori (Hp) in Qingd‐ao area to commonly used antibacterial drugs and to investigate the mutation characteristics of drug‐related resistant genes .Methods Hp was isolated from the mucosal samples of gastric antrum .The agar diffusion test was used to determine the susceptibility of Hp to clarithromycin ,levofloxacin and metronidazole .The 23s rRNA of clarithromycin resistance gene ,gyrA of levofloxacin resistance gene and rdxA of metronidazole resistance gene were amplified by using PCR ,after the PCR products sequencing ,the sequence com‐parative analysis was performed by the ClustalW2 software .Results The drug susceptibility test results found that the single re‐sistance rates of 134 strains of clinically isolated Hp to clarithromycin ,levofloxacin and metronidazole were 40 .3% ,34 .3% and 43 .3% ,respectively .Only 17 .9% of Hp strains were susceptible to these 3 kinds of antibacterial drug ;the multi‐drug resistance rate was 29 .9% ,triple drug resistance rate was 9 .0% ;furthermore ,the double resistance rate of levofloxacin plus metronidazole was significantly lower than that of clarithromycin plus levofloxacin ,the difference was statistically significant(3 .0% vs .10 .4% ,χ2 = 5 .96 ,P=0 .015) .The drug resistance genes sequence analyses showed that the commonest mutation locus was A2143G (77 . 8% ) ,the commonest mode of gyrA gene mutation was N87K(78 .3% ) ,and which of rdxA gene was nucleotide insertion into loci 20/32 ,generating the frameshift mutation with the mutation rate of 44 .8% .Conclusion The multi‐drug resistance rate of Hp is high in Qingdao area .The effective antibacterial drugs should be selected according to the drug susceptibility test results .Levofloxa‐cin could serve as the first line drug for the eradication therapy scheme in this area .